Method and apparatus for submarine well drilling, using a flexible tubing as drill string



DRILLING, USING A FLEXIBLE TUBING AS DRILL STRING Filed July 18, 1963 J.BER METHOD AND APPARATUS FOR SUBMARINE WELL 4 Sheets-Sheet l INVENTOR Fl9. 1

JEAN BER/V5 ATTORNEYS Sept. 7, 1965 J. BERNE 3, METHOD AND APPARATUS FORSUBMARINE WELL DRILLING, USING A FLEXIBLE TUBING AS DRILL STRING FiledJuly 18, 1963 4 Sheets-Sheet 2 INVENTOR JEA N BERNE ATTORNEY5 Sept. 7,1965 J. BERNE 3, 0 3 METHOD AND APPARATUS FOR SUBMARINE WELL DRILLING,USING A FLEXIBLE TUBING AS DRILL STRING Filed July 18, 1963 4Sheets-Sheet 3 5 INVENTOR JEAN BERNE ATTORNEYS Sept. 7, 1965 .1. BERNE3,204,708 METHOD AND APPARATUS FOR SUBMARINE WELL DRILLING, USING AFLEXIBLE TUBING AS DRILL STRING Filed July 18, 1963 4 Sheets-Sheet 4 PH34 F B Fig.6 Fig.7

INVENTOR c/EAN BER/YE ATTORNEY United States Patent C) 3,204,708 METHODAND APPARATUS FUR SUBMARINE WELL DRILLING, USING A. FLEXIBLE TUBING A'SDRILL STRING Jean Berne, Vernouiliet, France, assignor to InstitutFraucais du Ptrole des Carburants et Luhriiiants, Rueil- Malmaison,Seine-et-Oise, France Filed July 18, 1963, 'Ser. No. 296,066 Claimspriority, application France, July 24, 1962, 904,975 9 Claims. (Cl. 175-6) This invention relates to a method for carrying out submarine welldrilling with a flexible tubing as drill string and an apparatustherefor.

Submarine. well drilling at great depth is generally carried out with adrill string composed of a series of coupled rigid tube sectionsstarting from a ship at the water surface and placed substantially invertical alignment with the boring head.

Many problems arise, due to the presence of the waves,

of undercurrents and/ or climatic disturbances which tend on the onehand to move the ship away from its initial position and, on the otherhand, to subject the ship to vertical displacements corresponding to thehollows or the peaks of the waves.

In these conditions, it is diflicult to maintain the drill string in asubstantially vertical alignment with the well boring head, and thepermissible angle of the drill string with respect to said verticalalignment is relatively small. Furthermore, the movements of the shipmake it diflicult to adjust to the desired value the weight applied onthe drill bit.

One way of overcoming these difliculties consists of ad justing thelowering or the rising, with respect to the ships position, of the meansfor subjecting the drill string to a tensile strength, so that the ioadon the drill bit be kept substantially constant irrespective of theships displacements. However, the amplitude of the vertical displacementof the ship, depending on the sea condition and the type of the ship,may reach several meters.

The above method requires the use of a servoamechanism capable ofadjusting with a high accuracy (a few percent) the weight on the bitwhich may be as high as 20 to 30 metric tons.

Such a mechanism is very complex and also results in a considerableincrease of the cost of the drilling equipment.

Furthermore, this method for adjusting the weight on the drill .bitrequires a very restricted margin of movement for the ship.

In the case of deep drilling, the drill string must be kept permanentlywithin a cone having its peak at the well boring head and the ship mustbe so handled as to remain constantly inside the base of this cone. Inthis case, the margin for the angle of roll cannot be very large.

The method of drilling with the use of a flexible tubing avoids a partof the above-mentioned drawbacks due to the flexibility of the tubewhich results in a larger margin for handling the ship which may bemoved inside a larger cone base.

However, due to the fact that the load on the bit must be small, it hasto be adjusted with a greater accuracy, particularly in the case of deepdrilling. It is thus necessary to make use of complex servomechanisms inorder to maintain within the desired range the load on the bit and,accordingly, the traction strain on the flexible tubing.

It is therefore an object of this invention to carry out drillingoperations with the use of a flexible tubing in such a manner as toavoid the above-mentioned drawbacks.

It is another object of this invention to provide means for adjustingwith a satisfactory accuracy the load applied on the drill bit.

3,294,708 Patented Sept. 7, I965 It is still another object of thisinvention to considerably enlarge the margins for the ship displacementsin submarine drilling operations.

These and other objects as may be apparent from the followingspecification and claims are achieved by means of the method and deviceaccording to this invention whereby the total traction strain exerted:on the flexible drill string by traction means provided on the ship isreplaced by two separate traction strains, each applying to a separateportion of the drill string; one of these tract-ion strains, exerted onthe lower portion of the drill string to which is suspended the drillbit, being maintained substantially constant whereas the other tractionstrain exerted from the ship on the upper portion of the drill stringmay be of variable magnitude.

The traction strain exerted on the upper portion of the drill string isonly effective for balancing the weight of this tubing portion thelength of which is variable. As a matter of fact, as the drillingprogresses, new tubing lengths will be added to this upper portion ofthe tubing Whereas the lower portion will remain unchanged.

Moreover the total tubing length immersed must be suflicient to providefor a sufficiently wide margin for handling the ship and avoidingsurface disturbances (waves or the like) that have an eifect on theadjustment of the traction strain exerted from the ship.

Accordingly, the upper port-ion of the drill string will be placed alonga catenary curve whose end points are respectively the point ofapplication of the constant traction strain exerted on the lower portionof the drill string, and the point of application of the traction strainexerted from the ship. The lower point of this catenary curve dividesthe upper portion of the tubing into two arcuate partsthe greater ofwhich is supported from the ship, whereas the other, adjacent to thelower portion of the drill string is supported together with the latterby the constant traction strain.

Consequently, the weight on the drill bit will be equal to thediflerence between the weight of the assembly comprising the drill bit,the lower portion of the drill string having added thereto the adjacentarcuate part of the upper portion thereof and optionally drill collarsif any, in the one hand, and the traction strain on the other i and.

This weight on the drill bit will be kept substantially constantinasmuch as the Weight of the arcuate part of the upper portion of thedrill string which is adjacent to the lower portion thereof may beconsidered negligible as compared to the Weight of the latter.

An example of the method of the invention and of an embodiment ofapparatus for carrying out the same is hereafter described withreference to the accompanying drawings in which:

FIGURE 1 represents schematically the entire system by which the methodof this invention is put into practlce;

FIGURE 2 shows the winding mechanism for unwind ing the flexible cable;

FIGURE 3 shows the means for feeding electric current to the motor atthe bottom;

FIGURE 4 shows the means for adjusting the tractive force on thedrilling tool comprising a buoy whose buoyancy is regulated;

FIGURE 5 shows a mechanism for unwinding the cable that connects thebuoy to the flexible tube;

FIGURE 6 shows an apparatus actuated by variations of hydrostaticpressure for controlling the unwinding of the cable;

FIGURE 7 shows a buoy having a deformable side;

FIGURE 8 shows an accumulator of hydrostatic pressure; and

FIGURE 9 shows an apparatus for moving the point of attachment B of thetube to the cable which connects it to the buoy.

A flexible tubing ABCD ending with the drill bit F actuated for instanceby means of an electromotor G and located at point'A at the beginning ofthe drilling operation, is suspended from the ship at point D. A buoy Eimmersed at a sufficient depth to avoid the effect of the surfacedisturbances (a depth of the order of 30 meters for instance) and solocated as to be sheltered from undercurrents and in substantiallyvertical alignment with the boring head, exerts a constant tractionstrain on the portion AB of the flexible tubing, through theintermediary of a traction cable EB secured on the flexible tubing at apre-determined point B thereof. The upper portion of the flexible tubingbetween B and D (on the ship) must have a length slightly greater thanthe distance BD so that the tubing portion BCD takes on the shape of acatenary curve. When this is the case, and as it can be seen on thedrawing, the ship supports the weight of the portion DC of the drillstring, whereas the traction force exerted at point B by the buoybalances the weight of the lower part AB of the drill string togetherwith the electromotor and the drill bit as well as the weight of thetubing portion BC.

The feeding rate of the flexible tubing is adjusted so as to besubstantially equal to the depth drilled, whereby the tubing length BCis kept substantially constant.

Means for feeding the flexible tubing are illustrated by way of example,in FIGURE 2. This figure shows the flexible tubing 1 Wound on a reel 2rotatably mounted on a horiontal shaft 3 supported on a frame structure4.

This reel is driven by the motor 5 by means of belt or chain 6 passingover a pulley or sprocket wheel 7.

The feeding of electric current to the motor at the bottom isaccomplished by means of an electric generator 8.

The three conductors 9, 10 and Jill forming the cable 12 are connectedto the brushes 11 11 and b which are pressed against slip-rings c c andc respectively by springs carried by supports 4 (FIG. 3), the slip-ringsbeing mounted on the axis 3 of the reel and are insulated from the axisand from one another.

Three insulated conductors are connected to these sliprings and as shownin dotted lines, pass along the hollow axis to be connected at 13 to theend of a flexible threestrand conductor whose opposite end is connectedto the motor G at the bottom. Such a flexible conductor is described inUS. application Ser. No. 246,898 filed December 26, 1962.

Since the tubing length AB is invariable, the weight on the drill bit iskept constant inasmuch as the tubing length BC is also constant.

However, under the action of high amplitude waves, the point D maybemoved vertically by several meters from its mean position. The tubinglength corresponding to this amplitude variation is distributed by halfover the two arcuate tubing lengths BC and DC.

The variation of the traction strain at point B is therefore equal toone half of the weight of the tubing length corresponding to thedifference between BCD and distance BD, i.e. to the product of thislength difference expressed in meters for instance, by the weight permeter of the flexible tubing. Since the tubing length AB is constant,this variation will also be that of the weight applied to the drill bit,which variation is very small with respect to the amplitude of the shipdisplacement. When the drill bit is in operation, the tubing length ABremains constant and the point B moves downwardly towards the sea-bottomin proportion to the progression of the drill bit in the bore-hole. Asthe load on the bit depends on the length BC, it is convenient to keepthis length substantially constant by feeding the flexible tubing at anaverage rate equal to the speed of advance of the drill bit.

However, it may be more convenient, in the case for instance where thespeed of advance of the drill bit is low, to feed the flexible tubing ina discontinuous manner, in conformity with a time schedule, for instanceevery hour or half hour.

At each time, the adjustment is made by calculating the maximal tubinglength to be fed as a function of the maximum bearable load variation onthe bit.

The maximal load variation may be of i-5% under very limitativeconditions, which corresponds, in the case of a total load of 500 kgs.for instance, to a load variation on the bit of :25 kgs. If the weightof the flexible tubing used is, for instance, of 10 kgs. per meter, alength variation of 5 meters of the portion BC of the tubing length willbe acceptable, this variation corresponding to a 10 meter variation ofthe total tubing length.

Of these 10 meters of maximal variation of the total tubing length, 2 to3 meters will be kept free for instance in order to compensate for thevertical movement imparted to the ship, 2 meters for the lateraldisplacements which, in the case where the hanging point of the lowerportion of the tubing to the buoy is for instance at a depth of about2000 meters, corresponds to the possibility for the ship to move within:a circle having a radius of the order of a hundred meters. Of the 10meters, 5 to 6 are thus available for a periodical feeding of the tubefrom the ship, which may correspond, when drilling in hard formations,to a drilling period of the order of from one half hour to one hour.

The process of the invention thus provides for a large margin ofmovement of the ship together with a small variation of the load on thedrill bit. The latter may be determined with a high accuracy byadjusting the positive buoyancy of the buoy in accordance with thelength of the lower portion of the tubing. FIGURE 4 shows a conventionalapparatus for varying the actual floatability of the buoy E, or forkeeping it constant at a definite value.

This apparatus is formed of a caisson 14 having in its lower portion asingle opening 15 connected by a flexible tube 16 to a sliding member 17which can be moved along a threaded column 18 and with which the upperopen end of the tube is connected at 19. An electric motor 20 controlledfrom the surface through a cable 21 permits remote control of thevertical displacement of the sliding member along the guide rod 18.

A float 22 rests upon the level 23 of the water introduced through 19into the buoy. When the buoy moves down with the downward movement ofthe drill, the level 23 of the water in the buoy rises, lifting thefloat 22 which acts through the pivoted lever 24 to open the valve 25for admitting compressed air that was sent from the surface throughconduit 26.

The functioning is as follows: the sliding member 17 being in a fixedposition on the guide rod 18, the height of the water It in the buoytakes a value such that the float 22 would have a position correspondingto the opening limit of the valve and would remain in that position.

In fact, if the height It tends to increase beyond the value definedabove, in consequence of the lowering of the buoy, the float 22 willrise and open the valve 25 to admit compressed air into the buoy untilthe height h returns to its initial value. If, on the contrary, the buoyrises again, the water level in it is lowered and uncovers the opening19 of the tube 16 through which air then escapes, which, by lowering thepressure of the air, brings the water level to its original initialvalue.

In order to regulate from the surface the position of the sliding member17, the equilibrium height h in the buoy is regulated, and thereby theactual floatability of the buoy which corresponds to this height.

The pressure under which the air is introduced through conduit 26 shouldbe at least equal to the hydrostatic pressure existing at the level towhich the buoy is lowered. The surface equipment required therefor issimpler than that used in conventional earth boringthe accurate andcontinuous adjustment of the load on the bit being no longer necessary.The adjustment of the load on the bit is thus effected in a simplermanner than it is when drilling from the earth surface since in thislatter case, much more complicated means would be required for adjustingwith the same degree of accuracy the weight applied on the drill bit.

In proportion to the drilling advance, the buoy sinks to greater depths.This is not an inconvenience, provided that the mechanical strength ofthe buoy is sufficient. If, on the contrary, the buoy cannot withstandhigh pressures, it must be immersed only at the depth at which thehydrostatic pressure is lower than the maximal pressure that the buoymay sustain.

In this case, as the drilling electromotor progresses into the borehole, which results in the lowering of point B, the cable length BE willbe lengthened so as to main tain the buoy at a depth which is compatiblewith the maximal pressure that it may sustain.

This may be achieved by providing the buoy with a cable unreeling systemcontrolled by the variations of the hydrostatic pressure exerted on thebuoy. An automatic control of this type may be effected by means forinstance of a pressure gauge capsule. When the buoy depth is maintainedsubstantially constant by means of such an automatic control system, thedepth of point B may be determined at any time by measuring the unreeledcable length. An approximate value of this depth may also be deducedfrom the tubing length fed from the surface equipment on the ship.

FIGURE 5 shows a device for increasing from the surface the length ofthe portion BH of the cable and for measuring that portion.

This device comprises a windlass 27 with a substantial- 1y horizontalaxis situated at the lower end of the buoy.

The windlass is actuated, e.g. by an electric motor 28 controlled fromthe surface through conductors in a sheath 29. A conventionalrevolution-counter transmits its impulses to the surface through anelectric cable 31 contained in the same sheath 29.

The control of the unwinding of the cable BH can also be eflectedautomatically by hydrostatic pressure by replacing the motor 28 by aknown apparatus shown schematically in FIGURE 6. In the latter, therotation of the windlass 27 is controlled by a brake band L wrappedaround the rim of the drum and of which one end is connected to a fixedpoint 32. The other end of this band is connected to a piston 33 movablein a cylinder 34. One side of this piston is acted upon by a hydrostaticpressure PH While a calibrated spring 35 presses against the other side.

It can be easily seen that with this simple arrangement any increase ofhydrostatic pressure over the calibrated equilibrium pressure of theapparatus, which is caused by a lowering of the buoy E, will result in arelaxation of the drag of the brake L on the drum 27 and a consequentunwinding of the cable BH until the corresponding upward movement of thebuoy brings the hydrostatic pressure back to its initial value whichequilibrates the force of the calibrated spring 35.

According to another operating method, the cable length BE is notchanged and the buoy is allowed to lower by a depth corresponding to thedrilling advance. In this case, the buoy must be capable to sustain highpressures. A simple and economical type of structure for such a buoywould consist of a deformable casing filled up with a liquid having alower density than that of water. Such a deformable casing would not besubjected to pressure strains in view of its deformability.

FIGURE 7 shows schematically a buoy E having a deformable wall 36 andfilled with a liquid less dense than water.

However, such a type of buoy suffers from the drawback of being morevoluminous than a buoy of the preceding type providing for the sameupward force.

In this case, the depth of point B may be accurately 6 determined bymeasuring the hydrostatic pressure exerted on the buoy.

The telemetering of the hydrostatic pressure exercised.

on the buoy can be accomplished by means of a captive manometric deviceof the kind shown schematically in FIGURE 8 in which a bellows 37becomes deformed under hydrostatic pressure PH, which actuates a contactarm 38 of a potentiometer whose ends are connected to conductors 39 and40 under a constant potential difference. The potential at a point onthe surface of the potentiometer between the conductors 39 and 40 willthen be a function of the hydrostatic pressure. This potential istransmitted to the ship through conductor 41.

It must be noticed furthermore that, in view to avoid too numerouswithdrawals of the flexible drill string and the associated equipment,it may be convenient to provide means for displacing the point B of thetubing at which the same is hanged to the cable of the floating elementor buoy.

This displacement of point B may be effected during the drillingoperation for instance by means of a clamp ing device controlled byelectromagnetic means or by the hydrostatic pressure, or by use of acapstan supported from the buoy and having the flexible tubing woundthereon. The operation of this capstan may be adjusted, eithercontinuously or in a discontinuous manner, in proportion to the drillingadvance, for instance by con trol thereof from the floating element.

A displacement of the point B can be effected for example by means ofthe apparatus shown in FIGURE 9 in Which the conduit 1 is squeezedbetween two pairs of rollers 42 and 43 respectively, over which belts 44and 45 pass. At least one of these rollers is connected coaxially to anelectric motor 46 energized by a conductor which can be included in thecable BH. By controlling the current to the motor, the junction B can bemoved along the flexible tube any desired distance.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention and, withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Consequently, such changes and modifications are properly,equitably described and intended to be within the full range ofequivalence of the following claims:

What is claimed as this invention is:

1. A method for submarine well drilling, comprising the step ofsuspending a motor and a bit driven thereby from the lower end of aflexible tubing having an upper end at floating surface equipment,driving in the submarine soil said drill bit actuated by said motor,applying two traction strains separately to two portions of saidtubingone of the said strains, which is applied to the upper end of alower portion of invariable length of the tubing, ending with the drillbit, being maintained substantially constant, and the other strain,applied to an upper portion of variable length of the tubing, from asurface equipment, balances the weight of said upper portion.

2. A device for submarine well drilling by means of a drill bitsuspended from a flexible tubing used as drill string, comprising apower source, a bottom motor adapted to drive said bit, means fortransmitting energy from said power source to said bottom motor, afloating element immersed at a given depth and a cable suspending alower portion of said flexible tubing of invariable length, ending withthe drill bit, from said floating element, and means for so adjustingthe buoyance thereof as to support only a portion of the weight of thelower portion of the tubing, whereby a substantially constant upwardforce is applied to the upper end of said lower portion of the tubing.

3. A device according to claim 2 further comprising means for varyingthe length of said cable so as to maintain said given depth withinlimits compatible with the mechanical strength of said floating element.

4. A device, according to claim 2, wherein said cable is of invariablelength so that the depth of the floating element varies in proportion tothe drilling advance.

5. A device according to claim 3, wherein said means includes means forvarying the cable length in proportion to the depth drilled, whereby thefloating element is maintained at a substantially constant depth.

6. A device, according to claim 5, wherein said means for varying thecable length are controlled by the variations of the hydrostaticpressure exerted on the Walls of the floating element, and hydrostaticpressure responsive means for controlling the means for varying thecable length when said pressure exceeds a predetermined value.

7. A device, according to claim 5, wherein to said means for varying thecable length are associated measuring means of the resulting lengthvariations.

8. A device, according to claim 4, wherein the walls of the floatingelement are of a sufiicient mechanical strength to sustain thevariations of the hydrostatic pressure exerted thereon.

9. A device according to claim 4, wherein the floating element isprovided with deformable walls and further comprising a liquid having adensity lower than that of water, filling up said floating element.

References Cited by the Examiner UNITED STATES PATENTS 1,785,559 12/30Ponti 175-321 1,944,838 1/34 Hill 175-321 X 1,959,174 5/34 Moore 175-321X 2,512,783 6/50 Tucker 175-6 2,676,787 4/54 Johnson 175-7 2,783,0272/57 Gilbert 175-5 2,906,502 9/59 Smith 175-6 2,945,677 7/60 Karnmerer175-5 X 3,015,360 1/62 Stratton 175-7 X 3,017,934 1/62 Rhodes et al175-7 2/63 Moore 175-5 CHARLES E. OCONNELL, Primary Examiner.

1. A METHOD FOR SUBMARINE WELL DRILLING, COMPRISING THE STEP OFSUSPENDING A MOTOR AND A BIT DRIVEN THEREBY FROM THE LOWER END OF AFLEXIBLE TUBING HAVING AN UPPER END AT FLOATING SURFACE EQUIPMENT,DRIVING IN THE SUBMARINE SOIL SAID DRILL BIT ACTUATED BY SAID MOTOR,APPLYING TWO TRACTION STRAINS SEPARATELY TO TWO PORTIONS OF SAIDTUBING-ONE OF THE SAID STRAINS, WHICH IS APPLIED TO THE UPPER END OF ALOWER PORTION OF INVARIABLE LENGTH OF THE STANTIALLY CONSTANT, AND THEOTHER STRAIN, APPLIED TO AN UPPER PORTION OF VARIABLE LENGTH OF THETUBING, FROM A SURFACE EQUIPMENT, BALANCES THE WEIGHT OF SAID UPPERPORTION.